In recent years, in order to achieve a low carbon society, vehicles including a motor as a motive power source instead of a combustion engine or together with a combustion engine increase in number. Typical vehicles with a motor instead of a combustion engine include an electric vehicle (EV), and typical vehicles with a motor together with a combustion engine include a hybrid vehicle (HV). Such a vehicle includes a rechargeable storage battery (e.g., a secondary battery such as a lithium-ion battery or a nickel-hydrogen battery) which supplies electric power to drive the motor, and it is possible to charge the storage battery using electric power supplied from an external power unit.
In an electric vehicle or a hybrid vehicle (to be precise, a plug-in hybrid vehicle) being currently put to practical use, the electric power to charge a storage battery is generally transmitted through a cable connecting the vehicle and a power unit. In contrast, in recent years, a method in which electric power to charge a storage battery is wirelessly transmitted to a vehicle is proposed. In order to efficiently wirelessly transmit electric power, it is necessary to properly adjust the relative positional relationship between a power-transmitting coil (primary coil) provided in a power unit and a power-receiving coil (secondary coil) provided in a vehicle.
The following Patent Documents 1 to 6 disclose various methods to adjust the relative positional relationship between a primary coil and a secondary coil in order to efficiently perform the wireless power transmission. Specifically, Patent Document 1 discloses a technology to adjust the position of a secondary coil based on the detection result of a magnetic sensor which detects the position of a primary coil installed in the ground. Patent Documents 2 and 3 disclose technologies to adjust the position of a primary coil depending on the position of a secondary coil.
Patent Document 4 discloses a technology to guide a vehicle provided with a secondary coil to the optimum position when the vehicle is parked in a parking space, by displaying an image of a positioning marker captured by a camera provided in the vehicle on a display in the cabin thereof. Patent Document 5 discloses a technology to perform the positioning between a primary coil and a secondary coil by a member to be contacted which is provided in an unmanned transportation vehicle contacting a contacting member provided in a power supply unit. Patent Document 6 discloses a technology in which a secondary coil used to sense an intensity of electric power is provided in addition to another secondary coil to charge a battery and the positioning between a primary coil to charge the battery and the secondary coil used to charge the battery is performed based on the detection result of an intensity of electric power obtained by these secondary coils.